"Squamous cell metaplasia" in airway epithelium represents a change from the normal pseudo-stratified mucociliary epithelium to one in which the epithelial cells become flattened, usually stratified, and frequently keratinized. In vivo, squamous cell metaplasia of the respiratory tract is related to injury of epithelial cells induced by mechanical injury, vitamin A deficiency, and by exposure to carcinogens, toxic and infectious inhalants, and gases, such as tobacco smoke. The lesion has been implicated as an early sign of bronchogenic cancer development. Despite the recognition of this lesion as one of the hallmarks of airway epithelial cell injury, very little information regarding the molecular mechanism of the induction of such a lesion is available. During the last grant support period, we have demonstrated that the expression of a small proline-rich protein, spr1 and its related gene family, is associated with the early signs of squamous cell differentiation in airway epithelium. Spr1 and its related gene family have been shown to be associated with the superbasal cell layer of various squamous tissues, and they are involved in cornification. However, the expression of spr 1 and its related gene family is also very low, but detectable, in normal airway epithelium. The expression can be rapidly induced when epithelial cells are induced to express differentiated squamous cells. In this application, we will test the hypothesis that tissue- and cell type-specific mechanisms are involved in the regulation of spr1 gene and its gene family expression. We will also test the hypothesis that spr1 protein in airway epithelium have an additional role different from cornification, especially in cells that are not cornified. We have isolated and characterized the human spr1 gene structure. We have identified various motifs at the 5'-flanking region of the human spr1 gene and have characterized the responsive elements that are involved in vitro in the induction and activation of spr1 gene expression. A recent study, in which we collaborated with Dr. Ye-Shih Ho at Wayne State University, has demonstrated that the first 622 bp of the spr1 5'-flanking region contain the necessary information to direct the expression of a reporter gene, chloramphenicol acetyltransferase (CAT), in a tissue- and cell type-specific manner. To further elucidate this mechanism, we propose to carry out an additional transgenic mice study using different deleted or mutated promoter regions to direct tissue- and cell type-specific gene expression (Specific aim 1). Since squamous cell metaplasia can be induced by chronic tobacco smoke exposure, we will expose these transgenic mice to tobacco smoke to identify the cis-elements of the 5'-flanking region that are responsible for the induction (Specific aim 2). We will develop spr1 knockout transgenic mice to assess the role of spr1 in airway epithelium other than that involved in cell cornification (Specific aim 3).